Monolayer Ge₂Te₂P₄ as a promising photocatalyst for solar driven water-splitting: a DFT study

The buckling hexagonal structure of Ge₂Te₂P₄ was studied by first-principles calculations. The newly proposed structure was proven to be stable by analyzing its cohesive energy, phonon dispersion, elastic constants and AIMD results. Poisson's ratio of the Ge₂Te₂P₄ monolayer is in the range 0.16-0.18, and Young's modulus is in the range 40.16-43.74 N m^-1. The substituted Te atoms enhance the sp² orbitals which strengthen the σ-bonds and therefore the thickness of the Ge₂Te₂P₄ monolayer is smaller than that of monolayer GeP₃. The Ge₂Te₂P₄ monolayer has an indirect band gap of 1.85 eV, which can be narrowed by strains. The compressive band gaps from -2% to -4% change the electronic structure from the indirect band gap into the direct band gap. Strains can also increase the light absorption rate α(ω) in the visible region, which is 2-3 × 10⁵ cm^-1 at equilibrium. The Ge₂Te₂P₄ monolayer has a suitable band gap and an appropriate VBM and CBM position for hydrogen generation. Under strain rate of 4% and higher, the VBM and CBM remain at suitable positions for hydrogen production. Another advantage of the Ge₂Te₂P₄ monolayer is that its charge carrier mobilities are really high. The highest electron mobility is 1301.47 cm² V^-1 s^-1, and the highest hole mobility is 28627.24 cm² V^-1 s^-1, which are much higher than the mobility in monolayer GeP₃. The Ge₂Te₂P₄ monolayer has advantages for photocatalytic applications and it is necessary to perform further study on the material.